Molecular basis of chloroquine resistance. Genetic analysis has indicated that chloroquine resistance in P. falciparum is controlled by single gene or closely linked group of genes within a 200 kb segment of the parasite's seventh chromosome. We are isolating transcribe sequences from this segment and evaluating them as candidate chloroquine resistance genes. Other drug development targets. Studies have progressed on two Plasmodium enzymes: S-adenosylhomocysteine hydrolase (AHCY) and dihydrofolate reductase-thymidylate synthase (DHFR-TS). The P. falciparum AHCY has been expressed in E. coli for kinetic and functional comparisons with mammalian AHCY. Knowledge of point DHFR-TS mutations that produce resistance to pyrimethamine and cycloguanil is being used in PCR assays for epidemiological studies in Kenya and Mali. Transfection of Plasmodium erythrocytic stages. Efforts have focused transient expression experiments using luciferase and chloramphenicol- acetyl transferase (CAT) reporters flanked by control regions of the P. falciparum HRP-2 AND HRP-3 genes. Ballistic methods, lipofection and electroporation are being evaluated for DNA delivery. Genetic analysis of red cell invasion. A family of P. falciparum genes has been identified that encodes conserved domains known to be involved in red cell invasion. One of these genes (ebl-1) maps to a subtelomeric region of chromosome 13 that has been implicated in the efficiency of invasion. Preliminary evidence suggests that changes in expression of certain ebl genes may be associated with a switch between sialic acid- dependent and sialic acid-independent invasion pathways. Cytoplasmic inheritance in P. falciparum Unidirectional dominance in the inheritance mitochondrial-like and plastid-like genomes has been found in two genetic cross. Defective differentiation of male gametes occurred in a parent of one cross and is being mapped by linkage analysis.